The present invention relates to an electrically operated sound producing device and more particularly, to an electro-acoustic transducer especially adapted to be used in an alarm unit.
A wide variety of devices of the class to be described have been known in the prior art. Many of these devices have been specifically tailored to meet particular requirements of size, operating voltages, etc., and to meet certain costs and other manufacturing considerations.
In order to provide some background for the present invention, reference may be made to copending application Ser. No. 517,681, filed Oct. 24, 1974, now U.S. Pat. No. 3,931,549. The invention in that copending application relates to an electronic means for controlling an electro-acoustic transducer and for vibrating the diaphragm thereof at a frequency of the order of 2500 Hz. Although it is contemplated that the particular driving circuit described in the aforesaid copending application be used in conjunction with the present invention, the present invention is not necessarily limited to use only with such driving circuit.
Accordingly, it is a primary object of the present invention to improve significantly on the efficiency in the transfer of energy from electrical input to acoustical output for a class of devices designed to provide an alarm signal involving a substantially single frequency audio output.
It has been found that if the magnetic diaphragm utilized in the type of device under consideration is so supported as to be biased into a concave configuration, distinct advantages are obtained over a planar diaphragm. Thus, a better DB output is provided by the concave configuration since a lighter diaphragm can then be used and yet the concaveness will provide the frequency desired. Moreover, it has been found that a superior frequency response is obtained as will be made evident hereinafter. In addition, it has been found that the DB output for the concave configuration for the diaphragm is much more constant throughout the voltage range of operation. This advantage will also be made manifest as the description proceeds.
Further and other objects, advantages and features of the invention will be apparent from the following description of a preferred form of the invention as seen in the accompanying drawings.